August Evidence Corner

Dear Readers:   Wound needs seem simple: stop all causes of tissue damage, cleanse and debride if needed, protect from contamination, manage excess exudate, hydrate a dry wound, and maintain a moist wound environment.^1,2 Absorbent and specialty absorbent dressings help deal with excess fluid escaping the wound, but unseen fluid beneath an eschar or in interstitial spaces may pose an equal or greater danger to tissue repair or regeneration. What, if anything, is one to do when the excess fluid is concealed within local tissue or accumulates beneath a dried eschar? This Evidence Corner features two randomized controlled trials (RCT) researching very different ways to manage that hidden fluid. The first describes a cotton swab technique already taught in some medical universities that may help reduce the likelihood of surgical site infections (SSI) for clinicians practicing in settings with limited resources. The second study, an interim analysis, compares outcomes achieved using two different forms of vacuum to draw hidden fluid from a wound. One vacuum source requires electricity; the other does not. Laura Bolton, PhD, FAPWCA Adjunct Associate Professor Department of Surgery, UMDNJ WOUNDS Editorial Advisory Board Member and Department Editor

Probing Contaminated Surgical Incisions Reduces SSI

  Reference: Towfigh S, Clarke T, Yacoub W, et al. Significant reduction of wound infections with daily probing of contaminated wounds: a prospective randomized clinical trial. Arch Surg. 2011;146(4):448–452.   Rationale: Despite decades of research, no local therapy has been shown in a large RCT to reduce SSI for contaminated post-surgical incisions, such as those following an appendectomy for perforated appendicitis. Wound probing with a sterile cotton swab reduced SSI from a retrospective 24% to 4% for pediatric patients after heavily contaminated colorectal surgery. This procedure has not been studied in a prospective RCT.   Objective: Explore short- and long-term benefits of including a daily regimen of wound probing in the protocol for managing contaminated post surgical open appendectomy incisions loosely closed with staples.   Methods: A prospective, single-blind RCT conducted at a major California medical center included patients over 18 years of age who had undergone an open appendectomy within 24 hours before enrollment. All received standardized intravenous antibiotic therapy and daily incision swabbing with povidone iodine per the hospital appendectomy protocol. Subjects were randomized 1:1 to receive loose primary skin closure with staples placed at 2-cm intervals (control; n = 38) or the same closure plus daily wound probing ([WPP]; n = 38). WPP used a dry, sterile cotton-tipped applicator to blot fluid released from the incision while probing the incised skin and soft tissue between the skin staples to the depth of the external oblique fascia. The WPP was performed only once daily even if incision drainage continued. Quantitative swabs were taken on postoperative days 1, 3, and 5, as well as cultures of wound drainage for wounds with an ASEPSIS score over 20 and/or purulent drainage meeting the Centers for Disease Control and Prevention definition of nosocomial infection, in which case wounds were reopened to heal by second intention. Primary outcomes were incidence of postoperative SSI based on ASEPSIS score evaluated by clinicians blinded to treatment. Secondary outcomes were length of hospital stay, incision pain, and patient satisfaction evaluated 2 weeks and 3 months postoperatively.   Results: Patients in the two groups were comparable at baseline. WPP subjects had a shorter hospital stay (P = 0.049) and/or lower likelihood of wound infection (P = 0.03). Control subjects reached an ASEPSIS score of 0 earlier than the WPP group (P = 0.007), experiencing wider variation (0–20 days) than WPP subjects (0–7 days).   Authors’ Conclusions: Simple daily wound probing significantly reduced the incidence of SSIs in contaminated appendectomy incisions without increasing wound pain. Wound probing is recommended as first-line management of incisions after contaminated open surgery, such as bowel resection.

Comparing Vacuum Therapy Systems on Lower Limb Ulcers

  Reference: Armstrong DG, Marston WA, Reyzelman AM, Kirsner RS. Comparison of negative pressure wound therapy with an ultraportable mechanically powered device vs. traditional electrically powered device for the treatment of chronic lower extremity ulcers: a multicenter randomized-controlled trial. Wound Repair Regen. 2011;19(2):173–180.   Rationale: Non-healing chronic lower extremity wounds are a major healthcare problem. Negative pressure wound therapy (NPWT) has reported benefit in treating such wounds. Available NPWT devices include the widely used V.A.C.® Therapy System (KCI, San Antonio, TX) and one which delivers NPWT without using an electrically powered pump ([SNaP®], Spiricur, Sunnyvale, CA). Both have reported similar healing effects.   Objective: Directly compare SNaP and V.A.C. Therapy System effects on lower extremity wounds in a non-inferiority clinical trial with predetermined primary endpoints and a planned interim analysis.   Methods: Patients with a non-ischemic, non-infected, non-plantar lower limb venous or diabetic ulcer of at least 30-day duration were enrolled, screened for 2 weeks to rule out rapidly healing wounds, then randomized to V.A.C. or SNaP treatment for 4–16 weeks. SNaP and its gauze primary dressing (n = 27) were changed twice a week. The V.A.C. system and its foam primary dressing (n = 26) were changed at least three times a week. Advanced wound debridement (eg, ultrasound) was performed weekly or less frequently at the investigator’s discretion and held constant within investigator for each wound type across both NPWT groups. Standard 4-layer compression was used for all venous ulcers. Each center used its own standard off-loading orthotics for diabetic patients in both NPWT groups. Primary outcomes were percent of patients completely healed as analyzed by Kaplan-Meier survival analysis and percent decrease in wound area after 4, 8, 12, or 16 weeks of treatment. The last observation was carried forward for discontinued or healed patients. Secondary outcomes were time for dressing change and patient exit survey responses. The statistical analysis plan included an interim analysis qualifying SNaP as non-inferior to V.A.C. if the percentages healed at 16 weeks in both groups were less than 12.5 percentage points apart.   Results: In this interim analysis, 18 of 27 enrolled SNaP and 15 of 26 V.A.C. patients completed the full 16 weeks or healed. Two V.A.C. subjects whose wounds more than doubled in size were excluded as outliers. At 12 weeks, 36.7% of V.A.C. and 38.2% of SNaP subjects healed, increasing to 64.8% and 59.7%, respectively, at 16 weeks. There was no significant difference in the proportion of wounds healed over time (P = 0.99). These results confirmed that healing outcomes for the SNaP device were not inferior to those achieved with the V.A.C. Mean application time was 21 minutes for the V.A.C. and 11 minutes for the SNaP (P Authors’ Conclusions: For this subset of relatively shallow, non-plantar lower extremity wounds mainly secondary to venous disease, these results support similar efficacy for the gauze-based SNaP and the foam-based V.A.C. system. Further studies are needed to explore effects of foam- vs. gauze-based NPWT devices on deeper wounds with exposed subcutaneous structures.

Clinical Perspective

  Both of these studies managed fluid hidden beneath the wound surface that may act as a foreign body potentiating infection or accumulating edema impeding local circulation. Towfigh and colleagues confirm the value of a simple, low cost swabbing procedure to remove pockets of fluid formed beneath the surface of a loosely closed wound. Taught for years in some medical schools, daily gentle wound swabbing to express sub-incision fluid is earning its place in the post-surgical armamentarium. Future RCTs will define how often and firmly one should probe and why this works. Is the effect related only to minimizing fluid pooling or does it also reduce periwound edema and improve local circulation? Meanwhile, these authors took an important step toward establishing the fundamental value of WPP in preventing SSI following contaminated surgery.   Interim findings comparing the two NPWT devices confirm the US Department of Health and Human Services Agency for Healthcare Research and Quality³ conclusion that no single NPWT system or component has a significant therapeutic distinction in healing chronic wounds or reducing complications. NPWT has been shown to enhance repair of acute wounds, such as diabetic foot ulcer amputation sites⁴ compared to “moist wound therapy,” which included some dressings less moist than others. Could the mechanism of action relate to NPWT capacity to draw out pooled wound and interstitial fluid? Perhaps one day a RCT will explore NPWT device capacity to reduce SSI likelihood in contaminated post-surgical incisions or compare a NPWT system to the WPP swabbing procedure for the same purpose.   These findings open interesting questions for future research. What other ways might one allow sequestered fluids to flow from the wound? Could the moist autolytic environment beneath truly moisture-retentive⁵ film, hydrocolloid, or hydrogel dressings liquefy eschar or prevent its formation? This would remove eschar as a foreign body nidus for infection and open paths for fluid to emerge freely from the wound. Might this contribute to moisture-retentive dressings’ capacity to significantly reduce acute and chronic wound clinical infections compared to dry or impregnated gauze dressings?^6,7 Local wound management may be an important way to assure that sterling protocols of care are not subverted by microorganisms.

References

1. Beitz JM, van Rijswijk L. A cross-sectional study to validate wound care algorithms for use by registered nurses. Ostomy Wound Manage. 2010;56(4):46–59. 2. Bolton LL, van Rijswijk L. Wound dressings: meeting clinical and biological needs. Dermatol Nurs. 1990;2(3):146–161. 3. Agency for Healthcare Research and Quality. Negative Pressure Wound Therapy. Technology Assessment. November 2009. Rockville, MD: Available at: https://www.ahrq.gov/clinic/ta/negpresswtd/. 4. Armstrong DG, Lavery LA. Negative pressure wound therapy after partial diabetic foot amputation: a multicentre, randomised controlled trial. Lancet. 2005;366(9498):1704–1710. 5. Bolton LL. Evidence-based report card: operational definition of moist wound healing. JWOCN. 2007;34(1):23–29. 6. Hutchinson JJ, McGuckin M. Occlusive dressings: a microbiologic and clinical review. Am J Infect Control. 1990;18(4):257–268. 7. Wiechula R. The use of moist wound-healing dressings in the management of split-thickness skin graft donor sites: a systematic review. Int J Nurs Pract. 2003;9(2):S9–S17.